#include<iostream>
using namespace std;
int n;
bool is_prime(int x)
{
	for (int i = 2; i * i <= x; i++) {
		if (x % i == 0) {
			return 0;
		}
	}
	return 1;
}
int main()
{
	int t = 1;
	while (cin >> n) {
		if (n <= 0) {
			break;
		}
		if (n == 2 || n == 1) {
			cout << t << ": " << "no" << endl;
			t++;
			continue;
		}
		if (is_prime(n)) {
		    cout << t << ": " << "yes" << endl;
			t++;
		}
		else {
			cout << t << ": " << "no" << endl;
			t++;
		}
	}
	return 0;
}